Solar collector tube and a solar collector with multiple solar collector tubes

ABSTRACT

The object of the invention is a solar collector tube ( 2 ) for heating up gases, which comprises two tubes ( 21, 22 ) for forming a tube wall, disposed in a spaced-apart relationship so as to form an intermediate space, wherein the outer tube ( 21 ) is made of glass, a translucent synthetic material or composite material and the inner tube ( 22 ) is made of metal or a synthetic or composite material, wherein the solar collector tube ( 2 ) is open at both ends, at least in the region of the inner tube ( 22 ), for allowing passage of the gas to be heated.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority of registered German utility model No. DE 20 2014 001 094.3, filed Feb. 7, 2014.

FIELD OF THE INVENTION

The invention relates to a solar collector tube and a solar collector with multiple solar collector tubes.

Solar collector tubes are sufficiently known from the prior art. For example, DE 100 02 929 A1 discloses a solar collector tube, with which air or other gases are heated up in such manner that a medium with a sufficiently high temperature is provided. In detail, a double-walled tube is provided, which has an immersion tube in its centre, wherein there is a gap between the immersion tube and the double-walled tube, wherein a mesh serving as an absorber is disposed in the space formed by the gap. The medium to be heated is led through this absorber layer, wherein the medium heated in the partition wall is led back through the inside of the immersion_tube. This means that the known solar collector tube operates according to the counter-current exchange principle. Disposing multiple solar collector tubes on one conduit essentially leads to the formation of a parallel connection of multiple solar collector tubes for generating a correspondingly greater volume flow. This means that a parallel connection of a plurality of such solar collector tubes is not aimed at increasing the exit temperature of the heated gas, but at increasing the volume of gas exiting at a certain temperature. An increase of the temperature can be achieved by way of a series connection.

The document DE 198 21 137 B4 discloses a tube collector, which serves to heat up a liquid, more specifically water. To this end a so-called cladding tube is provided, wherein an absorber tube is disposed in the cladding tube at a distance from the cladding tube. A third tube, the so-called heat pipe, is located in the cladding tube. Cold water, which heats up over time on its way through the tube collector, is transported through the inside of this heat pipe, then exits the heat pipe at its end and is guided counter-current to a warm water return flow through the gap formed between the outer surface of the heat pipe and the inner surface of the absorber tube. This tube collector constitutes a self-contained unit, with which a certain amount of fluid can be heated to a certain temperature over a certain period of time depending on the radiation intensity.

In addition, so-called air collectors configured as flat-plate collectors are known from the prior art. Such flat-plate collectors are marketed for example by the company Grammer Solartechnik. In that air collector, a plurality of substantially rectangular tubes is provided, which form a collector when disposed next to each other. The tubes are made of aluminum_or synthetic material and are open at both ends. The collector has a cover made of a single-pane safety glass on its upper side, wherein the collector has a support in the form of a plate on its underside, wherein an insulating layer is provided between the plate-shaped support and the individual absorber tubes. When producing hot air, cold air is supplied at one end, and the hot air is taken off at the other end. A number of such collectors can be series-connected, since these collectors have respectively one flange frame on their front side.

The disadvantage of such Grammer collectors is that they provide a relatively low output while being relatively heavy and requiring a large surface for their installation. In this regard, these collectors have not prevailed for installation on flat roofs of industry buildings, precisely because their weight is too high in relation to the produced amount of heat.

In addition, there are solar collector tubes made of glass known as Sydney tubes. These tubes have two glass walls disposed in a spaced-apart relationship, wherein the one inner glass wall has an absorber layer. Such Sydney tubes serve to heat up fluids in that another tube holding the fluid is disposed in the Sydney tube. Since it is closed at one end, such a Sydney tube is not adapted to effectively heat up gases, because the volume flows are two low.

A solar collector tube in which the outer as well as the inner tube are made of glass is known from EP 2 322 871 A. Since glass must have a certain minimal thickness in order to be sufficiently solid, a solar collector consisting of two glass tubes disposed in a spaced-apart relationship is relatively heavy. In addition, there is always a risk that the inner tube will break due to high differences in temperature between the inner and outer tube.

SUMMARY OF THE INVENTION

Therefore, the problem underlying the invention is to provide a solar collector tube that is light and has a high degree of efficiency with regard to the produced amount of heated gas and is additionally solid.

In order to solve this problem, a solar collector tube for heating up gases is proposed, which comprises two tubes for forming a tube wall, disposed in a spaced-apart relationship so as to form an intermediate space, wherein the outer tube is made of glass, a translucent synthetic material or a translucent composite material and the inner tube is made of metal or a synthetic or composite material, wherein the solar collector tube is open at both ends, at least with regard to the inner tube, for allowing passage of the gas to be heated.

Glass tubes must have a minimal thickness of approx. 2 mm in order to reduce the risk of breakage. The thickness of the glass causes it to be heavy. An inner tube made of e.g. aluminum only requires a wall thickness of approx. 0.5 mm. Since glass and aluminum have about the same density, the total weight of the tube is smaller. Since, in the solar collector tube of the invention, the inner tube is still open at both ends, it is possible to let the gas to be heated pass through the tube and it is also possible to connect several such solar collector tubes in series, in order to further increase the output temperature. In order to produce a higher volume, it is also possible to connect multiple such solar collector tubes in parallel. Such solar collector tubes produced with an inner tube made e.g. of aluminum are relatively light and provide a high power output, which is why such solar collectors can also be installed as units on roofs of industrial plants in order to heat for example factory buildings by means of the heated air or to produce process heat.

It may be more specifically provided that the two tubes, i.e. the inner and the outer tube are connected to each other at their ends in a gas-tight manner for closing the intermediate space. This can be implemented for example by gluing together the two tubes at their ends in a temperature-resistant manner, wherein the bonding is such that differences in the thermal expansion of the two glass tubes can be compensated for. A high-temperature-resistant bonding of the two tubes, for example by way of silicone glue is conceivable.

In order to increase the temperature in such a solar collector tube, the inner tube has an absorber. More specifically, the tube is provided with an absorber layer. In detail, it can be provided in this context that the absorber layer is disposed on the inner side or on the outer side of the inner tube. If the absorber layer is disposed on the outer side of the inner tube, the consequence will be that the inner tube, e.g. made of aluminum, will be strongly heated, and will consequently expand correspondingly more than the outer glass tube. On the other hand, with an inner tube made of a non-translucent material, e.g. aluminum, the absorber layer can only be fastened to the outer side.

As has already been explained elsewhere, a compensation of such different expansions caused by different temperatures can be implemented by way of an appropriate adhesive bonding between the outer and the inner glass tube. However, it is also possible to use a compensator, which means that the inner tube made for example of aluminum has a circumferentially wave-shaped or folded or meandering configuration, preferably in an end region, in order to allow for movement in case of thermal expansion.

In addition, it may be provided to arrange heat conduction plates in the inner tube of the solar collector tube. The heat conduction plate, which can be inserted into the inner tube of the solar collector tube in any configuration, preferably rests on the inner wall of the inner tube. It is welded, soldered or only pressed onto the inner tube. In any case, a contact between the heat conduction plate and the inner wall of the inner tube is expedient with regard to the heat transfer. Such a heat conduction plate increases the surface for transferring heat from the inner tube to the gas flowing through it.

In order to also achieve a heating of the air volume transported in such a solar collector tube or in a plurality of such series-connected solar collector tubes in the cold season, it is provided that the intermediate space between the inner tube and the outer tube is configured in such a manner that the heat lost due to radiation is reduced. This can be achieved on the one hand by evacuating the space between the two tubes, i.e. the outer and the inner tube, or by filling it with a lowly heat-conductive gas, for example xenon or argon.

If only low temperatures are needed, the air can also be left in the intermediate space. In this regard, the tube can be adapted to the appropriate temperature requirements.

A solar connector with multiple solar collector tubes of the type mentioned in the introduction, wherein the multiple solar collector tubes are connected to each other by sleeves is also an object of the invention. It has already been mentioned elsewhere that when the solar collector tubes are heated up, an expansion caused by the increase in temperature is to be expected. In this regard, in order to connect the solar collector tubes with each other, it is provided in particular that the sleeves, which are made of an elastomer, have a T-shaped configuration, wherein the web of the sleeve is located between the front tube walls of two adjacent solar collector tubes. The limb of the sleeve surrounds the wall of the respective solar collector tube in the manner of a cuff, which means that such a sleeve is first slid onto the solar collector tube until it abuts with its web against the front side of the solar collector, wherein the other solar collector tube is subsequently also slid into the open limb of the sleeve. The height of the web is chosen so that it corresponds approximately to the wall thickness of the two inner and outer tubes forming the wall plus the distance between the two tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is exemplarily described in more detail based on the drawings.

FIG. 1 shows a solar collector in a perspective representation;

FIG. 2 shows a detail from FIG. 1 of a magnified representation of a section of a first embodiment;

FIG. 3 shows a detail from FIG. 1 of a magnified representation of a section of another embodiment;

FIG. 4 shows a detail from Fig. 1 of a magnified representation of a section of a third embodiment;

FIG. 5 a-5 c show different embodiments of a solar collector tube with differently configured heat conduction plates; and

FIG. 6 shows the inner tube with a compensator based on the example of the embodiment according to FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS

The object of the invention is the arrangement of the individual solar collector tubes (FIG. 2 to FIG. 5). Such a solar collector tube labelled 2 comprises the two tubes 21 and 22 fitted inside one another in a spaced-apart manner. The intermediate space 23 between the two tubes is closed at one end, either by way of a temperature resistant bonding 25, for example by means of silicone glue, or, when both tubes are made of the same material, by fusing the ends of both tubes 21, 22 as schematically shown in FIG. 3. In the representation according to FIG. 2, the absorber layer labelled 28 is disposed on the inner side of the inner tube 22, whereas in the embodiment according to FIG. 3, the absorber layer 28 can be found on the outer side of the inner tube 22.

According to FIG. 4 inserting an inner tube 22, e.g. made of a composite material, configured as an absorber, is also conceivable. The absorber can have any shape. The connection between the two tubes can also be carried out by means of temperature-resistant silicone glue 25.

A sleeve 10 is provided for implementing a series connection of solar collectors with solar collector tubes. The sleeve labelled 10 grasps the two series-connected solar collector tubes 2 plus the gap between the two tubes. The sleeve 10 comprises the web 11 as well as the two limbs 12 and 13. The height of the web 11 corresponds to the wall thickness 29 of the solar collector tube 2 formed by the two glass tubes 21 and 22. The limbs 12 and 13 of the sleeve 10 each grasp the respective solar collector tube 2 by its outer surface as can be seen in the representations according to FIGS. 2 and 3.

FIGS. 5 a to 5 c additionally show the arrangement of a heat conduction plate 30 in the inner tube 22. The plate can have any shape and be connected to the inner wall of the inner tube. For example it can be welded or pressed onto the inner wall so that it cannot be displaced.

FIG. 6 shows the configuration of an inner tube 22 with a compensator, which can have a wave-shaped, folded or meandering configuration. The inner tube 22 will become warmer, which is why it will expand more that the outer tube 21. The compensator 24 is provided in order to compensate for the differences in the lengthwise expansion of the tubes. The compensator is preferably located in the end region of the inner tube.

A solar collector configured in the manner described above is characterized by a relatively low total weight, while having a high power output. For example, a solar collector of the type shown in FIG. 1 with a surface of 25 m² is able to produce up to 23 kW of power (depending on the insulation), while having a weight of approximately 310 kg. This means that such a solar collector can also be mounted on flat roofs with a relatively low permissible roof load and can still provide a sufficient heating output for heating a factory building. The heated air cannot only be used for heating purposes but also as process heat.

REFERENCE NUMERALS

-   1 solar collector -   2 solar collector tube -   10 sleeve -   11 web -   12 limb -   13 limb -   21 outer tube -   22 inner tube -   23 intermediate space -   24 compensator -   25 bonding -   28 absorber layer -   29 wall thickness -   30 heat conduction plate 

1-17. (canceled)
 18. A solar collector tube for heating up gases, comprising: an outer tube, wherein the outer tube is made of a material selected from the group consisting of glass, a translucent synthetic material and a translucent composite material, an inner tube, disposed inside the outer tube in a spaced-apart manner, having a hollow space defined inside the inner tube, wherein the inner tube is made of a material selected from the group consisting of metal, a synthetic material and a composite material; the outer tube and the inner tube cooperating to form a tube wall; an intermediate space defined between the outer tube and the inner tube; and wherein the inner tube is open at both ends, for allowing passage of the gases to be heated through the hollow space.
 19. The solar collector tube according to claim 18, wherein the inner tube and the outer tube are connected to each other at their ends in a gas-tight manner for closing the intermediate space.
 20. The solar collector tube according to claim 18, further comprising an absorber layer.
 21. The solar collector tube according to claim 18, wherein the inner tube is made of an absorber material.
 22. The solar collector tube according to claim 20, wherein the absorber layer is a coating.
 23. The solar collector tube according to claim 20, wherein the absorber layer is disposed on an outer side of the inner tube.
 24. The solar collector tube according to claim 18, wherein the outer tube and inner tube are connected to each other at least at one end.
 25. The solar collector tube according to claim 24, wherein the outer tube and the inner tube are glued to each other in a temperature-resistant manner.
 26. The solar collector tube according to claim 18, further comprising a heat conductor for transferring the heat from the inner tube to the gas passing through the inner tube, wherein the heat conductor is disposed in the hollow space of the inner tube.
 27. The solar collector tube according to claim 18, wherein the intermediate space is evacuated.
 28. The solar collector tube according to claim 18, wherein the intermediate space is filled with a low heat-conductive gas.
 29. The solar collector tube according to claim 28, wherein the gas is argon.
 30. The solar collector tube according to claim 18, wherein the inner tube has a compensator.
 31. The solar collector tube according to claim 30, wherein the compensator has a wave-shaped, folded or meandering configuration.
 32. A solar collector with multiple solar collector tubes according to claim 18, wherein the multiple solar collector tubes are connected to each other by sleeves.
 33. The solar collector according to claim 32, wherein the sleeves have a T-shaped cross-section.
 34. The solar collector according to claim 32, wherein each sleeve has two limbs and a web, the web of the sleeve being located between the tube walls of two adjoining solar collector tubes and one limbs of the sleeve surround the tube wall of the respective solar collector tube in a manner of a cuff.
 35. The solar collector according to claim 32, wherein the sleeve is made of an elastomer or another synthetic or composite material. 